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Subject[PATCH -tip 4/6 V4] x86: kprobes checks safeness of insertion address.
Ensure safeness of inserting kprobes by checking whether the specified
address is at the first byte of a instruction. This is done by decoding
probed function from its head to the probe point.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/kprobes.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d..39c79cc 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -48,12 +48,14 @@
#include <linux/preempt.h>
#include <linux/module.h>
#include <linux/kdebug.h>
+#include <linux/kallsyms.h>

#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
+#include <asm/insn.h>

void jprobe_return_end(void);

@@ -244,6 +246,53 @@ retry:
}
}

+/* Recover original instruction */
+static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
+{
+ struct kprobe *kp;
+ kp = get_kprobe((void *)addr);
+ if (!kp)
+ return -EINVAL;
+
+ /* Don't use p->ainsn.insn; which will be modified by fix_riprel */
+ memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+ buf[0] = kp->opcode;
+ return 0;
+}
+
+/* Dummy buffers for lookup_symbol_attrs */
+static char __dummy_buf[KSYM_NAME_LEN];
+
+/* Check whether the address can be probed */
+static int __kprobes can_probe(unsigned long paddr)
+{
+ int ret;
+ unsigned long addr, offset = 0;
+ struct insn insn;
+ kprobe_opcode_t buf[MAX_INSN_SIZE];
+
+ /* Lookup symbol including addr */
+ if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf))
+ return 0;
+
+ /* Decode instructions */
+ addr = paddr - offset;
+ while (addr < paddr) {
+ insn_init_kernel(&insn, (void *)addr);
+ insn_get_opcode(&insn);
+ if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) {
+ ret = recover_probed_instruction(buf, addr);
+ if (ret)
+ return 0;
+ insn_init_kernel(&insn, buf);
+ }
+ insn_get_length(&insn);
+ addr += insn.length;
+ }
+
+ return (addr == paddr);
+}
+
/*
* Returns non-zero if opcode modifies the interrupt flag.
*/
@@ -359,6 +408,8 @@ static void __kprobes arch_copy_kprobe(struct kprobe *p)

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
+ if (!can_probe((unsigned long)p->addr))
+ return -EILSEQ;
/* insn: must be on special executable page on x86. */
p->ainsn.insn = get_insn_slot();
if (!p->ainsn.insn)
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com



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